In semiconductor manufacturing facilities, commonly known as fabs, highly corrosive, ultra pure liquids are utilized in manufacturing operations. Conventional plastics and metallic tubing and plumbing components are highly unsuitable in these applications. The materials of choice for plumbing components are fluoropolymer plastics such as PFA and PVDF because of their chemical inertness and non-wettability. The plumbing components will typically comprise tubing, valves, fittings, filters, sensors, tanks and the like. Fluids that are handled may include slurries with suspended abrasive materials used for polishing semiconductor wafers. Such polishing must be carefully controlled and uniform over the surface of the wafer. It is desirable for plumbing that handles such slurries to have transitions that are as smooth as possible to minimize the formation of eddy's or quiescent zones in which suspended materials may fall out of suspension. Smooth fluid flow avoids creating the possibility of a non-uniform distribution of abrasive and consequent uneven polishing of wafers. Uneven polishing creates unusable wafers and loss of yield. Thus, smooth transitions are preferred in any fitting which changes the direction of fluid flow to keep suspensions uniform. U.S. Pat. No. 6,399,006 B1 discloses an approach to manufacturing sweep fittings and is incorporated herein in its entirety by this reference.
Conventional standard elbows have a sharp inside corner. The presence of the sharp inside corner can create a substantial pressure loss and consequently, a substantial decrease in flow rate as compared to flow through an equivalent sized straight tube. Further, the sharp corners of a standard elbow create areas of turbulence and eddying. Turbulence and eddy currents can cause particulate matter suspended in slurries to fall out of suspension and accumulate in areas of slow fluid flow. Accumulated particulate matter may build up in these areas and slow the fluid flow through the conduit as well as create the possibility that lumps of particulate matter may break loose from the accumulation and be carried with the flowing fluid. These lumps will destroy the uniformity of a polishing suspension and lead to expensive loss of yield in the wafer production process.
Sharp transitions also create increased friction between flowing fluid and the conduit. Pressure drop within the system lowers flow rates and slows processing. Compensating for pressure drop requires an increased pressure at the head of the system. This produces the need for more powerful pumps and increases stresses on components in the portions of the system where pressures are higher increasing the risk of failure.
Turbulence also creates the possibility that cavitation will occur. Cavitation tends to create increased wear on the surfaces of conduit walls shortening the life of components.
In addition, space is at a premium in modern manufacturing facilities. It is thus preferable that fittings be as small as possible in order to provide for efficient usage of available space. The availability of smaller fittings improves the system layout and efficiency.
Thus, it would be a substantial benefit if fittings were available to provide smooth fluid flow along with minimal turbulence. In addition, it would be a benefit if the fittings were as compact as possible in order to allow a reduced footprint for connection of tubing.